While many today would say that any misfortune surrounding a production is mere coincidence, actors and other theatre people often consider it bad luck to mention Macbeth by name while inside a theatre, and sometimes refer to it indirectly, for example as “the Scottish play”, or “MacBee”, or when referring to the character and not the play, “Mr. and Mrs. M”, or “The Scottish King”.

This is because Shakespeare (or the play’s revisers) are said to have used the spells of real witches in his text, purportedly angering the witches and causing them to curse the play. Thus, to say the name of the play inside a theatre is believed to doom the production to failure, and perhaps cause physical injury or death to cast members. There are stories of accidents, misfortunes and even deaths taking place during runs of Macbeth. (Wikipedia)